Members of an enterprise may be provided with mobile stations that are able to communicate via both cellular networks and wireless local area networks (WLAN). While such a device is within the coverage area of an enterprise WLAN (eWLAN) or a public WLAN, a private branch exchange (PBX) of the enterprise may be able to route communication sessions between the mobile device and other communication devices via the eWLAN or the public WLAN, respectively. In addition, while such a device is within the coverage area of a cellular network, the PBX may be able to route communication sessions between the mobile device and other communication devices via the cellular network.
There is a tradeoff between WLAN detection latency and the power consumption required of the mobile station, i.e., the power consumption goes up with the rate at which the WLAN radio is activated to search for WLAN access points (APs). Unfortunately good responsiveness is difficult to obtain without severely impacting the power consumption of the mobile station. This problem is exacerbated by the fact that Institute of Electrical and Electronic Engineers (IEEE) 802.11h has requirements for passive scanning until the mobile station determines its current regulatory jurisdiction. Passive scanning involves leaving the WLAN radio on in receive mode long enough to ensure that any AP beacons will be received with high probability. This is normally a much more power intensive process than using active scanning. The power consumption problem will also worsen as the number of WLAN channels increases, which will happen as handsets are equipped with IEEE 802.11a radios.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.